Hydrogenolysis of polyhydric alcohols obtained from the natural world using a catalyst for converting the polyhydric alcohols into other compounds is an important technique from the viewpoint of effective utilization of materials or substances.
On the other hand, production of glycerol used as the polyhydric alcohol in food or medical applications has been increased year by year. One of the reasons therefor is the spread of bio-diesel fuels which have recently come to dominate owing to uncertain supply of fossil fuels or global warming problems. Glycerol is produced during the process for production of the bio-diesel fuels from raw vegetable materials. However, excessive supply of the glycerol has occurred due to currently limited applications thereof. Therefore, effective utilization of the glycerol has been demanded. As one solution of the above problem, a catalytic reaction of the glycerol for converting the glycerol into C3 alcohols has been noticed over the world.
The C3 alcohols are useful as various industrial materials, etc. Among the C3 alcohols, as diols, there are 1,3-propanediol and 1,2-propanediol. The 1,3-propanediol has been noticed as a raw material of polyesters and polyurethanes, etc.
On the other hand, the 1,2-propanediol (hereinafter occasionally referred to merely as “1,2-PD”) has been used, for example, for production of polyester resins, paints, alkyd resins, various plasticizers, anti-freezing fluids, brake oils, etc., and further are useful for production of food wetting agents, viscosity increasers for fruit juices, cellophane softeners for food, cosmetics, drugs, etc.
In order to effectively utilize glycerol, there have been proposed various methods for producing 1,2-PD by hydrogenolysis of the glycerol.
For example, as the hydrogenolysis of glycerol using a catalyst, there are known (1) the method using a nickel-rhenium/carbon catalyst (for example, refer to Patent Document 1), (2) the method using a ruthenium/carbon catalyst (for example, refer to Patent Document 2), (3) the method using a copper-zinc/alumina catalyst (for example, refer to Patent Document 3), (4) the method using a copper-zinc oxide catalyst (for example, refer to Patent Document 4), (5) the method using a copper-chromium catalyst (for example, refer to Non-Patent Document 1), (6) the method using a ruthenium catalyst (for example, refer to Patent Document 5), and the like.
However, these conventional methods are still unsatisfactory because of a low conversion rate of glycerol, a low selectivity to 1,2-PD, etc. In particular, under the low-pressure condition which is generally advantageous for practicing industrial methods, it tends to be difficult to achieve both a high reactivity of the glycerol and a high selectivity to 1,2-PD. Thus, the conventional methods have failed to attain satisfactory levels of the reactivity and the selectivity. In addition, in Non-Patent Document 1 and Patent Document 5, there is described such an effect of water that the selectivity to the aimed product is considerably deteriorated if no water is previously added to the reaction system.
Patent Document 1: PCT Pamphlet WO 03/035582
Patent Document 2: EP-A 523014
Patent Document 3: EP-A 523015
Patent Document 4: DP-A 4302464
Patent Document 5: JP-A 2007-283175
Non-Patent Document 1: Applied Catalysis A: General, 281, 225, (2005)